Mammalian myristoyl CoA: protein N-myristoyltransferase

Myristoyl CoA:Protein N-myristoyltransferase (NMT) is the enzyme which catalyses the covalent transfer of myristate from myristoyl CoA to the amino-terminal glycine residue of protein substrates. Although NMT is ubiquitous in eukaryotic cells, the enzyme levels and cellular distribution vary among tissues. In this article, we describe the properties of mammalian NMT(s) with reference to subcellular distribution, molecular weights, substrate specificity and the possible involvement of NMT in pathological processes. The cytosolic fraction of bovine brain contains multiple forms of NMT activity whereas bovine spleen contains only a single form. In bovine brain and spleen, the cytosol contained majority of NMT activity. In contrast, rabbit colon and rat liver NMT activity was predominantly particulate. Regional differences in NMT activity have been observed in both rabbit intestine and bovine brain. Results from our laboratory along with the existing knowledge, provide evidence for the existence of tissue specific isozymes of NMT.     

Oligosyndactyly: A lethal mutation in the mouse that results in mitotic arrest very early in development

The mutation, oligosyndactyly, results in syndactyly, muscle anomalies, and diabetes insipidus in heterozygous mice. When homozygous, the mutation is lethal early in development. Although homozygous embryos are able to form blastocyst outgrowths (the in vitro equivalent to implantation), cells begin to accumulate in mitosis as early as the blastocyst stage. Even though the cytologic appearance is that of mitotic cells treated with a microtubule inhibitor such as colcemid, the homozygous embryos do, in fact, have normal appearing mitotic spindles. These results define the Os mutation as one which, in the homozygous state, prevents the movement of chromosomes from the metaphase plate. It is the first mammalian developmental mutation to be so defined and is unique among all mitotic arrest mutations thus far described in higher eucaryotes.     

Non-linear regression of biological temperature-dependent rate models based on absolute reaction-rate theory

Biological temperature-dependent rate models based on Arrhenius' and Eyring's equations have been formulated by Johnson & Lewin (1946), Hultin (1955), and Sharpe & DeMichele (1977). The original formulation of Sharpe and DeMichele is poorly suited for non-linear regression. Very high correlations of parameter estimators occassionally make regression with their equation impossible using Marquardt's algorithm (1963).This analysis describes a new formulation of Sharpe and DeMichele's model that greatly alleviates the non-linear regression problem. It is partly based on Hultin's formulation (1955). Biological and graphical interpretation of the model parameters is discussed. Regression suitability is illustrated with a typical data set. Similar modifications to the equations of Hultin (1955) and Johnson & Lewin (1946) are described.     

A time-dependent mathematical expression of the münch hypothesis of phloem transport

A time-dependent mathematical expression of the Münch, osmotically driven mass flow hypothesis of phloem transport is presented. The dependent variables include concentration of solutes, pressure, velocity of phloem sap, osmotic flux of water, and concentration dependent unloading of solutes. The model meets conservation requirements during all iterations, and responds realistically to changes in independent variables. Given the same set of independent variables the time-dependent model converges to the same values as the closed-form steady-state model of Goeschl et al. (1976) regardless of the initial conditions.     

Membrane phase transitions and the transport of chlortetracycline.

When chlortetracycline is added to a suspension of respiring Staphylococcus aureus cells, the active transport of the antibiotic may be monitored by its fluorescence enhancement as it moves from a polar aqueous environment into the apolar regions of the membrane. The initial rates of transport are temperature dependent with a maximal rate between 35 and 45 °C. Arrhenius plots of the initial rates are biphasic with a transition temperature of 27 °C for control cells. This transition temperature is sensitive to the fatty acid composition of the S. aureus cells. By culturing the cells in the presence of oleic acid or at 10 °C, the S. aureus cells incorporate a larger percentage of unsaturated and branched chain fatty acids into their membranes, resulting in transition temperatures 8–9 °C lower than the control cells. Studies of depolarization of fluorescence also indicate that the mobility of the bound chlortetracycline is temperature-dependent. Temperature transitions occur at the same temperatures as those measured by Arrhenius plots. The transition temperatures indicated by the Arrhenius plots and the polarization studies are believed to reflect order-disorder phase transitions associated with the melting of the phospholipids in the cell envelope.     

Functional UQCRC1 polymorphisms affect promoter activity and body lipid accumulation

Obesity and type 2 diabetes constitute leading public health problems worldwide. Studies have shown that insulin resistance affiliated with these conditions is associated with skeletal muscle lipid accumulation, while the latter is associated with mitochondrial dysfunctions. However, the initiation and regulation of mitochondrial biogenesis rely heavily on approximately 1000 nuclear-encoded mitochondrial regulatory proteins. In this study, we targeted the ubiquinol-cytochrome c reductase core protein I gene, a nuclear-encoded component of mitochondrial complex III, for its association with subcutaneous fat depth (SFD) and skeletal muscle lipid accumulation (SMLA) using cattle as a model. Four promoter polymorphisms were identified and genotyped on approximately 250 Wagyu x Limousin F2 progeny. Statistical analysis revealed that two completely linked polymorphic sites, g.13487C>T and g.13709G>C (r2 = 1), were significantly associated with both SFD (p < 0.01) and SMLA (p < 0.0001). The difference between TTCC and CCGG haplotypes was 0.178 cm for SFD and 0.624 scores for SMLA. Interestingly, the former haplotype produced higher promoter activities than the latter by 43% to 49% in three cell lines (p < 0.05). In addition to Rett syndrome and breast/ovarian cancer observed in other studies, we report evidence for the first time, to our knowledge, that overexpression of ubiquinol-cytochrome c reductase core protein I might affect mitochondrial morphology and/or physiology and lead to development of obesity and related conditions.     

Trophoblast–endothelium signaling involves angiogenesis and apoptosis in a dynamic bioprinted placenta model

Trophoblast invasion and remodeling of the maternal spiral arteries are required for pregnancy success. Aberrant endothelium–trophoblast crosstalk may lead to preeclampsia, a pregnancy complication that has serious effects on both the mother and the baby. However, our understanding of the mechanisms involved in this pathology remains elementary because the current in vitro models cannot describe trophoblast–endothelium interactions under dynamic culture. In this study, we developed a dynamic three-dimensional (3D) placenta model by bioprinting trophoblasts and an endothelialized lumen in a perfusion bioreactor. We found the 3D printed perfusion bioreactor system significantly augmented responses of endothelial cells by encouraging network formations and expressions of angiogenic markers, cluster of differentiation 31 (CD31), matrix metalloproteinase-2 (MMP2), matrix metalloproteinase-9 (MMP9), and vascular endothelial growth factor A (VEGFA). Bioprinting favored colocalization of trophoblasts with endothelial cells, similar to in vivo observations. Additional analysis revealed that trophoblasts reduced the angiogenic responses by reducing network formation and motility rates while inducing apoptosis of endothelial cells. Moreover, the presence of endothelial cells appeared to inhibit trophoblast invasion rates. These results clearly demonstrated the utility and potential of bioprinting and perfusion bioreactor system to model trophoblast–endothelium interactions in vitro. Our bioprinted placenta model represents a crucial step to develop advanced research approach that will expand our understanding and treatment options of preeclampsia and other pregnancy-related pathologies.